CODEWITHSUNDEEP
javajava-8
user09
user09

Reputation: 956

Sort and check if numbers are in consecutive order using Java8

I am trying to sort a list of longs and validate if the numbers are in consecutive order starting from 1. I want to do everything in java8/streams

//sorting first
 List<Long> sortedNums = request.stream().map(Request::getSequence)
                .collect(Collectors.toList()).stream().sorted().collect(Collectors.toList());

//getting first num to see if the seq starting from 1
Optional<Long> first = sortedNums.stream().findFirst();

        if (first.isPresent()) {
            if (first.get() != 1) {
                throw new BadRequestException("Sequence should start from 1");
            }
        }
//checking if the list is in consecutive order
 if(!isConsecutive(sortedNums)) {
            throw new BadRequestException("Sequences should be in consecutive order");
        }
 private boolean isConsecutive(List<Long> list) {
        for (int i = 1; i < list.size(); i++) {
            if (list.get(i - 1) + 1 != list.get(i)) {
                return false;
            }
        }
        return true;
    }

I am trying to see if there is more optimal way of doing this with stream combining all the statements into one or two.

Upvotes: 1

Views: 1806

Answers (1)

Eritrean
Eritrean

Reputation: 16498

I would do this in different small methods instead of one where you do everything:

public static boolean startsWith1(List<Long> list){
    //return list.stream().sorted().findFirst().get() == 1; //see @Holger's comment
    return Collections.min(list) == 1;
}
// The sum of all numbers from 1 to n = n * (n+1) /2; 
// you can use that to check if your list contains all numbers from 1 to n
public static boolean isConsecutive(List<Long> list){
    long n = list.size();
    return list.stream().mapToLong(Long::longValue).distinct().sum() == n * (n+1) /2;
}
public static void doSomething(List<Long> list) throws BadRequestException{
    if(!startsWith1(list)){   
        throw new BadRequestException("Sequence should start from 1 ");
    }
    if(!isConsecutive(list)) {
        throw new BadRequestException("Sequences should be in consecutive order");
    }
    else{
        // do whatever with your list
    }
}

Upvotes: 1

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